Since no real contract exists, this is speculation on my part: In one of the early chapters, we learn that the major decisions of the band are made by majority vote with each member having an equal share. This means the vote they took in his absence where three of the four members agreed would be sufficient to stop a lawsuit BUT an image is all about the public perception and nothing about what's right in most cases so the threat of a lawsuit may be enough to get the brothers to try negotiating with